1. Field of the Invention
This invention relates to a novel optical modulating method and more particularly a novel optical modulating method utilizing the phase transition phenomenon of a polymeric substance which is caused by temperature change.
2. Related Background Art
Heretofore, recording or displaying using light has been widely practiced. One method for modulating light for this purpose is disclosed, for example, in Japanese laid-open patent publication No. 5523/1981 describing a modulation process by changing the electrical field distribution within a crystal having an electrochemical effect and diffracting the light introduced onto the portion of the crystal where the refractive index is changed by the electrical field distribution.
On the other hand, light modulation has also recently been a refractive index distribution based on thermal effect. Such methods are reported in "Deflection of Light by Refractive Index Change by Heat" (Nikkei Electronics, Aug. 16, 1982) and "Response Speed of TO Glass Waveguide Type Optical Switch" (All-Japan Meeting of Electronic Communication Society, 1982).
It has been also reported that a heat-sensitive material comprising an acrylamide-type polymer and water undergoes a sharp phase change between a transparent phase and an opaque phase around room temperature and that the temperature at which such change occurs can be freely set by controlling the composition of the material. The such application of the phenomena to temperature-sensitive light-shielding material, thermometer, etc., has also been considered.
Generally speaking, not only an acrylamide-type polymer but also many other polymeric substances are known to exhibit a phenomenon wherein the molecular chains transform from a random coil into a globule in an appropriate solvent around a specific temperature. This phenomenon is accompanied by change in optical properties, and since the energy required for such a change is small, this material can be preferably used for the purpose of optical modulation. Accordingly, the present inventors have already proposed an optical modulating device utilizing the phase transition phenomenon by temperature change of these polymeric substance-containing solution in U.S. patent application Ser. No. 810,249.